The overall objective of this proposed research is to investigate the role of Staphylococcus aureus cytotoxin in experimental burn wound infections. Although S. aureus has been demonstrated to elaborate many extracellular toxic products, the role of these toxic products in the pathogenesis of burn wound infections is largely unknown. Preliminary studies in our laboratory have indicated that culture filtrates of S. aureus burn isolates caused extensive cytotoxicity in human foreskin cells and in human epidermis. Our studies have shown that this cytotoxicity was attributed to a large molecular weight (253,000 daltons) S. aureus cytotoxin. When one of these burn isolates was applied to burned skin of mice, we observed that this organism grew and proliferated on the burned site; moreover, this organism also invaded the underlying tissues. Skin of control animals, however, had markedly less bacterial colonization and little damage to the epidermis. We also demonstrated that skin extracts from S. aureus-infected, burned animals contained a toxic factor that exhibited a dose-related cytotoxic response for human foreskin cells; however, this cytotoxic response was neutralized by antiserum to the large molecular weight cytotoxin. These observations suggest the involvement of in vivo S. aureus cytotoxin in experimental burn wound infections. Thus, initial efforts will be directed toward purifying and characterizing this S. aureus cytotoxin using a series of chromatography procedures. Monospecific antitoxin to the purified cytotoxin will then be produced and used as an immunological probe to detect the presence of in vivo cytotoxin in skin and in vital organs of mice undergoing experimental burn wound infection. Burn wound infection due to S. aureus strains has been difficult to control because of the emergence of many antibiotic-resistant strains. In view of this, alternate therapeutic and preventive measures are needed for the control and prevention of this infection in burned patients. Hence, once the role of this S. aureus cytotoxin in burn infection is clarified, attempts will be made to evaluate the immunoprophylactic potential of the antitoxin. If this antitoxin is found to have protective effects for experimental burn animals, future immunization studies can be designed and consequently could lead to the production of vaccines for use in severely burned patients.